Apparatus and method for non-destructive testing of materials

ABSTRACT

A device for testing a test material for defects within the test material has an acoustic broadband transducer offset from the test material surface during testing by a distance so that the transducer acquires acoustic waves across an air gap from the test material, wherein the acoustic waves arise from impact of an impact member on the test material.

The present application is a continuation of U.S. application Ser. No.14/855,208, filed Sep. 15, 2015 (now U.S. Pat. No. 10,126,271), theentire disclosure which is incorporated by reference herein.

BACKGROUND

The present invention relates to the use of acoustic waves in thenon-destructive testing of materials.

Methods and devices are known that utilize the propagation and receptionof acoustic waves for testing characteristics of materials used in theformation of a variety of products, for example rotary wings, aircraftfuselages, nacelles, aircraft control surfaces, honeycomb sandwichstructures, composite turbine fan blades, automotive passenger cells,automotive body panels, sailboat spars and masts, and boat hulls.

Carbon fiber-reinforced polymer (CFRP) materials and structures are ofincreasing importance in the aerospace, automotive, and otherindustries, due to their light weight and high strength. In modernaircraft, the fuselage and wings can be made from more than 50%composite materials, for example based on carbon fiber sheets and/orincluding sandwich structures formed by carbon fiber composite sheetsdisposed on opposing outer surfaces of an aluminum honeycomb centerstructure. As should be understood in this art, other compositestructures may be used, for example formed by fiberglass sheets onopposing sides of a NOMEX core. The strength of such composite materialsmay be compromised by degradation caused, for example, by impact damage,fatigue, and thermal damage during service, as well as defects createdby faulty manufacturing. Defects may include delamination of a compositesheet forming one or the other side of a sandwich structure or bondfailure between a core material (for example, the aluminum honeycomb orNOMEX cores discussed above) and the outer composite sheets(disbonding). Such defects are often not identifiable by visualinspection.

To determine these defects in such materials, it is known to place atransducer on the material and strike the material with an impact hammerto thereby generate mechanical waves in the material that are detectedby the transducer. The transducer outputs a corresponding signal tocircuitry that digitizes the signal and converts the signal to thefrequency domain, and a processor analyzes the resulting data for signalstructures indicating a defect. It is also known to house apiezoelectric transducer in a hand-held housing so that when the housingis placed against the test material, a surface of the piezoelectrictransducer abuts the outer surface of the test material. It is necessaryto maintain the piezoelectric transducer in highly direct acousticcontact with the material surface, and an acoustic coupling gel may bedisposed on the transducer surface and in direct contact with thematerial surface for this purpose. Upon the user's actuation of acontrolling processor, the processor actuates the piezoelectrictransducer, causing the transducer to impart an acoustic signal into thetest material and the processor to receive a resulting signal from theoutput of the piezoelectric transducer. The processor analyzes theresulting signal to identify presence of defects in the material.

The present disclosure recognizes and addresses the foregoingconsiderations, and others, of prior art constructions and methods.

SUMMARY OF THE INVENTION

A device protesting a test material for defects within the test materialaccording to an embodiment of the present invention has a housing, anacoustic broadband transducer housed by the housing, and an engagementportion of the housing defined with respect to the acoustic broadbandtransducer so that a distal end of the engagement portion defines asurface that is offset from a receiving portion of the acousticbroadband transducer. An impact member defining an impact portion andbeing is housed by the housing so that the impact portion is moveablefrom a retracted position to the surface. The surface is offset from thereceiving portion of the acoustic broadband transducer by a distance atwhich the acoustic broadband transducer is capable of acquiring acousticwaves across and air gap from a test material at the surface. Theacoustic waves arise from impact of the impact portion of the impactmember with the test material upon movement of the impact portion of theimpact member to the surface. A processor system is in communicationwith the impact member and the acoustic broadband transducer so that theprocessor system, in response to receipt of an actuation signal,actuates the impact member to drive the impact portion from theretracted position to the surface, and so that the processor systemreceives a first output signal from the acoustic broadband transducercorresponding to the acoustic waves that arise from impact of the impactportion with the test material at the surface.

In a method of testing a test material for defects within the testmaterial in an embodiment of the present invention, a test device isprovided having a housing, an acoustic broadband transducer housed bythe housing, and an engagement portion of the housing defined withrespect to the acoustic broadband transducer so that a distal end of theengagement portion defines a surface that is offset from a receivingportion of the acoustic broadband transducer. An impact member definingan impact portion is housed by the housing so that the impact portion ismoveable from a retracted position to the surface. The surface is offsetfrom the receiving portion of the receiving broadband transducer by adistance. The test device is placed so that the engagement portionengages a test material at the surface. The impact portion of the impactmember is moved to the surface so that the impact portion of the impactmember impacts the test material. The acoustic broadband transduceracquires acoustic waves across an air gap from the test material. Theacoustic waves arise from impact from the impact portion of the impactmember with the test material.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate one or more embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, directed to oneof ordinary skill in the art, is set forth in the specification, whichmakes reference to the appended drawings, in which:

FIG. 1A is a perspective exploded view of a data acquisition unit andprocessor unit of a device for determining the presence of defects in atest material according to an embodiment of the present invention;

FIG. 1B is a perspective exploded view of a signal acquisition unit foruse with the data acquisition unit and processing unit of the device asshown in FIG. 1A as part of the device for determining the presence ofdefects in a test material;

FIG. 1C is a perspective view of the signal acquisition unit as shown inFIG. 1B;

FIG. 1D is a perspective view of the signal acquisition unit as shown inFIG. 1B;

FIG. 1E a perspective view of the signal acquisition unit as shown inFIG. 1B having four rolling ball feet;

FIG. 2 is a schematic block diagram of control circuitry comprising thedata acquisition unit and signal acquisition unit as in FIG. 1A and FIG.1B;

FIG. 3 is a graphical illustration of signals generated by the signalacquisition unit of FIG. 1B, processed by the data acquisition unit asin FIG. 1A for frequency domain-based analysis, and analyzed by theprocessing unit as in FIG. 1A;

FIG. 4 is a flow diagram of operations of the data acquisition unit,processing unit, and signal acquisition unit of FIGS. 1A and 1B; and

FIG. 5 is a perspective view of a signal acquisition unit as in FIGS.1B-1E in use with a composite material that may be tested for presenceof defects by the system, with the composite material shown in asectional perspective view.

Repeat use of reference characters in the present specification anddrawings is intended to represent same or analogous features or elementsof embodiments of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made in detail to one or more embodiments of thepresent invention, one or more examples of which are illustrated in theaccompanying drawings. Each example is provided by way of explanation ofthe invention, not limitation of the invention. In fact, it will beapparent to those skilled in the art that modifications and variationscan be made in the present invention without departing from the scopeand spirit thereof. For instance, features illustrated or described aspart of one embodiment may be used on another embodiment to yield astill further embodiment. Thus, it is intended that the presentinvention covers such modifications and variations as come within thescope of the present disclosure.

As used herein, terms referring to a direction, or a position, such asbut not limited to “vertical,” or “horizontal,” “upper,” refer to themeaning of those terms with respect to the Earth and others, such as“lower,” “above,” or “below,” with respect to the signal acquisitionunit, refer to directions and relative positions with respect to theunit's orientation in its normal intended operation when engaging ahorizontal test surface. Thus, such terms should be understood in thatcontext, even with respect to a signal acquisition unit that may bedisposed in a different orientation.

Further, the term “or” as used in this application and the appendedclaims is intended to mean an inclusive “or” rather than an exclusive“or.” That is, unless specified otherwise, or clear from the context,the phrase “X employs A or B” is intended to mean any of the naturalinclusive permutations. That is, the phrase “X employs A or B” issatisfied by any of the following instances: X employs A; X employs B;or X employs both A and B. In addition, the articles “a” and “an” asused in this application and the appended claims should generally beconstrued to mean “one or more” unless specified otherwise or clear fromthe context to be directed to a singular form. Throughout thespecification and claims, the following terms take at least the meaningsexplicitly associated herein, unless the context dictates otherwise. Themeanings identified below do not necessarily limit the terms, but merelyprovide illustrative examples for the terms. The meaning of “a,” “an,”and “the” may include plural references, and the meaning of “in” mayinclude “in” and “on.” The phrase “in one embodiment,” as used hereindoes not necessarily refer to the same embodiment, although it may.

Referring to FIGS. 1A-1E, a hand-held device 10 for identifying defectsin a composite material 15 (see FIG. 5), for example a wall of anaircraft engine or fuselage (for instance, an aluminum honeycombstructure 19 sandwiched between respective top and bottom CFRP compositesheets 21 a and 21 b, as shown in FIG. 5), includes a signal acquisitionunit 12, a data acquisition unit 14, and a controller or processing unit16. Referring particularly to FIGS. 1B and 1C, signal acquisition unit12 includes a clamshell type construction defining opposing halves 17 aand 17 b, each made from a glass-filled NYLON 12 or other suitablethermoplastic or other material that forms a water tight device housingby a molding or other suitable process. Clamshell half 17 b definesthree connecting bosses 18, each defining a respective aperture 20surrounded by a corresponding gasket. A circuit board 22 defines threeholes 24 that respectively align with holes 20 and bosses 18 so thatwhen board 22 rests upon the distal ends of bosses 18, holes 24 alignwith holes 20. Clamshell half 17 a includes three pins (not shown)disposed correspondingly to holes 20 and 24 so that when mold half 17 ais fitted to mold half 17 b, the pins extend through holes 24 and intoholes 20, securing the clamshell halves together. A shoulder surface andcorresponding gasket (not shown) about each pin at clamshell half 17 aabuts board 22 about the respective holes 24 so that, when clamshellhalves 17 a and 17 b are assembled, board 22 is held securely in placebetween the clamshell halves. Referring also to FIG. 2, circuitryindicated at 22 in FIG. 2 is disposed on board 22 as shown in FIG. 1B,including an LED display 26 that, when unit 12 is assembled, extendsthrough an aperture 28 in clamshell half 17 a. A pair of push buttons 30and 32 are secured in clamshell half 17 a above aperture 28. Asdescribed in more detail below, these buttons communicate with circuitryon board 22 to provide a mechanism by which the operator may increaseand decrease impact strength of a hammer mechanism held by clamshellhalf 17 b.

Corresponding outer edges of clamshell half 17 a and 17 b mate with eachother to thereby form a closed interior volume in which the componentsdiscussed herein are housed. A gasket 34 lines the edge of clamshellhalf 17 b to form a water tight seal with the corresponding outer edgeof half 17 a. A similar gasket is provided about the edge of aperture 28to sealingly engage LED display 26. A cut out portion 36 of clamshellhalf 17 a mates about a correspondingly curved surface 38 of a LEMO,TURCK or other suitable cable connector 40. A gasket is provided aboutsurface 38 to maintain the seal between the clamshell halves. When unit12 is assembled, connector 40 extends a cable 134 (see FIGS. 2 and 5)connecting to it in a horizontal direction, or in a direction transverseto axes 66 and 68 (discussed below) of the device transducer and hammer.More generally, connector 40 is disposed, and extends cable 134 from, aside 41 of housing 17 of signal acquisition unit 12 that is transverseto a lower face 44 of unit 12.

Each clamshell half holds a respective rolling ball bearing bolster 42extending from lower face 44 of signal acquisition unit 12. The ball ineach bolster 42 is secured axially in its respective bolster housing 46so that the ball may roll freely about any axis but may not movevertically within the bolster housing. Thus, the two balls 42 definefeet of unit 12 that engage the material surface under test by unit 12.Each clamshell half also defines a respective non-rolling bolster 48formed in a semi-spherical shape with an outer (lower, in theperspective of FIG. 1B) surface covered with or made of a low-frictionmaterial, for example DELRIN, capable of sliding on the expected testmaterial. The vertical distance from face 44 to the distal ends of feet48 is the same as the vertical distance from face 44 to the distal endsof ball feet 42 so that, when signal acquisition unit 12 is disposed onthe bolsters on a planar surface, the broadband transducer (amicrophone, as described below) surface is disposed in a parallelposition above the test material surface. The bolsters/feet define anengagement portion of the housing of signal acquisition unit 12 in thatthey engage the test material surface (see the surface of uppercomposite sheet 21 a, in FIG. 5) when the unit is in operation for atest, as shown in FIG. 5. The four distal ends of bolsters 42/48 definea plane. While the actual test material surface the bolsters engage fora test may, as described below, vary from a planar configuration, thebolster ends may be considered to define a planar surface for purposesof discussing the configuration of unit 12 herein. Although thisembodiment includes two rolling ball-type bolsters 42 and twonon-rolling bolsters 48, it should be understood that otherconfigurations are possible, e.g. four non-rolling bolsters or fourrolling ball bolsters, and FIG. 1E illustrates the signal acquisitionunit of FIGS. 1B-1D having four rolling ball bolsters 42.

A bracket 50 secured within clamshell half 17 b secures a connectingboss between the clamshell halves. A further bracket secures a solenoidunit 52 that drives a hammer 54, as described in more detail below. Thehousing of solenoid 52 secures a spring that engages hammer 54 tothereby bias hammer 54 upward, away from the test material surface (seethe surface of composite material 21 a, FIG. 5) and the surface definedby the bolster ends. Solenoid 52 also includes a coil surrounding anupper arm of hammer 54 that is selectively actuated, as described below,by delivery of electric current through the coil to thereby drive hammer54 downward, against the spring bias, away from face 44 and toward thesurface defined by the bolster ends so that a distal end, or impactportion, 56 strikes the test material surface located at the surfacedefined by the bolster ends. A TEFLON ring 58 surrounds an outercircumference of the lower portion of hammer 54 and is slidinglyreceived within a correspondingly-shaped molded portion (not shown) ofclamshell half 17 a that acts as a guide to maintain up-and-downmovement of hammer 54 and minimize vibrations from such movement.

A second bracket (not shown) in clamshell half 17 b secures a microphoneassembly 60 that defines a broadband receiving transducer surface 62 atface 44. Microphone 60 is an electronic condenser microphone having, inthis embodiment, an acoustic bandwidth within range of about 2 kHz toabout 25 kHz or to about 30 kHz. An example of such a microphone isprovided by PUI Audio, Inc. of Dayton, Ohio, under part no. PUM-3564L-R.While the frequency range of 2 kHz to 30 kHz is discussed herein withinthe context of the presently-described embodiments, it should beunderstood that this is for purposes of example only and that theoperative frequency range may vary depending upon the desired use of agiven device. In general, and within the microphone/transducer operablefrequency range, the ability to detect higher frequency acoustic signalswithin that operable frequency range requires that the system detectsignals having correspondingly shorter wavelengths. This may, in turn,affect selection of the separation between the hammer and the microphonetransducer. For instance, the p-wave that the microphone/transducer isintended to detect is generated by a signal originated by the hammer andthat travels in the test material in directions generally along thehammer axis as indicated at 68. The p-wave's front width varies withwavelength. Accordingly, in certain embodiments, the hammer and themicrophone transducer are disposed sufficiently close together that thesystem can detect the acoustic p-wave signals generated from impactsfrom the system's hammer at resonant frequencies within the fulloperative frequency range of the microphone/transducer, and morespecifically at the high end of the transducer's operative frequencyrange, which corresponds to the short end of the wavelength range.

In the presently-described embodiments, microphone 60 and hammer 54 aredisposed at face 44 so that they are separated by a center-to-centerdistance of about 0.5 inches. Orienting the device so that the hammer isdirectly over the defect during the test maximizes the likelihood ofdetecting the defect. In certain embodiments as described herein, whereaxes 66 and 68 respectively of microphone transducer 60 and hammer 54(where axes 66 and 68 are parallel to each other and perpendicular tothe transducer face) are separated by about 0.5 inches, the system candetect defects with widths (in a plane perpendicular to axes 66 and 68)of about 0.25 inches. Thus, where hammer 54 is directly over the defect,the microphone may be offset from the defect.

Clamshell half 17 b secures an infrared transmitter 70 that is receivedin a corresponding cut out 71 (FIG. 1C) in a top portion of clamshellhalf 17 a. Also on the top of clamshell 17 a is an LED display 72 havingLEDs capable of distinctly displaying the colors red, yellow, and green.A start-stop button 74 is provided on a front face of clamshell half 17a.

Referring also to FIG. 1A, data acquisition unit 14 comprises a circuitboard 76, and associated circuitry disposed thereon, secured within amolded housing 78 made from a glass-filled NYLON 12 or other suitablethermoplastic. Housing 78 defines a lower face 80 having an aperture(not shown) into which fits a plate 82 to which is secured a tray 84 toreceive one or more batteries (not shown), for example six “AA” typebatteries. Plate 82 is secured by a plurality of screws (not shown) thatextend through holes in bushing portions 86 in cap 82 and that arethreadedly received in threaded female anchor portions (not shown)formed in or attached an interior portion of housing 78. A lower capplate 85 covers the bottom of the unit.

The batteries (not shown) held by tray 84 provide power to the circuitryon board 76 and may provide power to processing unit 16. A fuse 88 issecured to an inner portion of housing 78 and communicates with a powercircuit that includes the batteries in tray 84 and the circuitrydisposed on board 76. Fuse 88 protects the components of the dataacquisition unit and processor unit by disconnecting power flow from thebatteries at high-current events, as should be understood. Housing 78defines an open top end 90 over which fits a mobile device bracket 92that is secured to an upper edge of housing 78 by screws (not shown)that extend through holes 94 and are threadedly received bycorresponding threaded bores 96 along the edge of housing 78. Anelectrical conduit 98 extends through bracket 92 to allow electricalcommunication between processing unit 16 and data acquisition unit 14,as described below. Bracket 92 defines a recess 100 shaped to receiveprocessing unit 16, which in this embodiment is a “smart phone” typemobile computing device having a processor and touch screen 102, asshould be understood in this art. One example of a smart phone that maybe used for this purposes is a GALAXY S4 ACTIVE available from SamsungElectronic Company, Ltd., of Yongin-si, Gyeonggi-do, Korea, although itshould be understood that other processor-based circuitry may be used,including tablets and dedicated embedded circuitry. A jack 104 attachedto the smart phone connects to a cable (not shown) that extends throughconduit 98 to facilitate communications between a processor (not shown)of processing unit 16 and a processor of data acquisition unit 14.Processing unit 16 may operate from power provided by a battery internalto unit 16 or, optionally, from line power provided by a cableconnection via an input port 121 from an external source or, asdescribed below, from the data acquisition unit.

An upper cap plate 106 covers processing unit 16 and holds processingunit 16 within recess 100. Cap plate 106 defines an aperture 108 sizedcorrespondingly to touch screen 102 and other control features on device16 to provide user access to the touch screen and other controls. Capplate 106 is secured to plate 92 and housing 78 by screws (not shown)that extend through holes 110 in cap plate 106 and correspondingthrough-holes 112 in plate 92 to be threadedly received in correspondingthreaded bores 114 in housing 78.

A power connection port 116 is provided on a side of housing 78 toprovide an optional access point at which to provide power from anexternal line power source to the circuitry of the data acquisitionunit. When line power is applied to the unit via connector 116,actuation of a master/slave switch 117 causes circuitry on board 76 todraw power from line power connector 116 rather than from the batteriesof tray 84. In another embodiment, circuitry on board 76 recognizes thepresence of line power at 116 and responsively automatically draws powerfrom the line power connector, rather than the batteries, without needfor switch 117. In either arrangement, when applied to data acquisitionunit, line power may supersede the battery power and may be provided toprocessing unit 16, as noted below, and to data acquisition unit 12 (viaa power line in communication cable 134, as shown in FIGS. 2 and 5).

A USB port 127 disposed in the side of housing 78 communicates with thepower circuitry that draws power from the batteries stored in tray 84 orline power from jack 116. The USB 2.0 port can receive an electricalcable that attaches at its other end at input port 121 of the smartphoneof processing unit 16 that is accessible through a gap 123 provided inupper cap plate 106 so that the smartphone battery may be optionallyrecharged from the batteries of unit 14 or from line power. An on-offbutton 125 controls a switch that communicates with the circuitry ofdata acquisition unit 14 to activate and deactivate device 10, includingdata acquisition unit 14, processing unit 16, and signal acquisitionunit 12. Button/switch 125 directly actuates actuation circuitry onboard 76, the processor of which forwards actuation signals to units 16and 12 via communication paths discussed below. Alternatively, the usermay activate processing unit 16 through a control provided with thesmartphone. An application on the smartphone, in turn, forwards anactuation signal to unit 14, which forwards an actuation signal to unit12. A cable connector 128 receives the opposing end of a communicationcable 134 (FIGS. 2 and 5) attached to cable connector 40 (FIG. 1B).Cable connector 128 electrically communicates with a processor of dataacquisition unit 14, and cable connector 40 is in electricalcommunication with a processor of signal acquisition unit 12, so thatthe two processors communicate via the cable indicated at 134 in FIG. 2and cable connectors 128 and 40.

The discussion herein makes reference to the user uploading data from,or possibly downloading data or software to, system 10 and particularlyprocessing unit 16. While it should be understood that variousmechanisms may be used from those purposes, in the presently illustratedembodiments the user uploads data from unit 16 to an independentcomputing system though a wireless Internet or other network connection(e.g. using BLUETOOTH or other protocol) from, or by a cable connectedto a port of, processing unit 16. The user may upload data to, ordownload data or software from, the independent computer system directlyor via an intermediate data storage provider. For such purposes, theuser may interact with an application provided with and executed byprocessing unit 16 via touch screen 102, to select the desired data toupload to or download from the independent computer system. Undercontrol of the application, and when the wireless connection isestablished or when the cable is connected to and between unit 16 andthe independent computer system, processing unit 16 and the independentcomputer system communicate so that processing unit 16 recognizes thepresence and availability of the independent computer system to receiveor send the data or software. Processing unit 16 may be operated in thisfashion while attached within the data acquisition unit housing but mayalso be removed from the housing and used separately from the dataacquisition unit for data and software exchange, if desired. Theprotocols and programming methods for communication between such devicesshould be well understood and are, therefore, not discussed in furtherdetail herein.

In the presently described embodiment, housing 78 is 8.6 inches inlength by 5 inches in width, by 2.9 inches in height, and has a weightof approximately 1.75 pounds. These dimensions and weight facilitate auser's ability to carry housing 78, and therefore data acquisition unit14 and processing unit 16, by hand while simultaneously operating signalacquisition unit 12, holding signal acquisition unit 12 in the user'sother hand. The housing of signal acquisition unit 12 is about 3.6inches in height, about 2.6 inches in general diameter (cable connector40 extends about 1.6 inches from the SAU housing's center axis), andabout six ounces in weight. The SAU is thus easily hand carried and handactuatable, though it should be understood that the SAU's size andweight can vary. A cable (indicated at 134 in FIG. 2) extending betweencable connectors 128 and 40 is approximately ten feet in length.Alternatively, a strap may be provided that attaches to a ring 131secured to a corner of housing 78, so that the user may hang the dataacquisition unit and processing unit over the user's shoulder by thestrap while operating the signal acquisition unit with one hand andleaving the user's other hand free. Still further, ring 131 may beattached to a clip or other attachment device attached to the user'sapparel.

As noted above, the distal ends of bolsters 42 and 48 (or of fourbolsters 42 or four bolsters 48) define a planar surface that isparallel with the receiving surface of the broadband transducer ofmicrophone 60 and is separate or offset from the microphone receivingsurface by a distance, in this embodiment, of about 0.1 inches orgreater. Because the microphone transducer receiving surface is offsetfrom the material test surface by an air gap, as opposed to anintervening acoustic coupling material, the resulting acoustic impedancemismatch between the test material surface and the air gap lowers thesignal power received by the microphone transducer, as compared to thesignal power received by a transducer acoustically coupled to the testmaterial surface by a coupling gel. The received power can be increasedby reducing the air gap distance, but on the other hand, increasing thegap distance provides greater accommodation for surface irregularities.Thus, the particular air gap distance can vary to accommodate theseand/or possibly other considerations. The air gap separation between themicrophone transducer receiving surface and the expected test materialsurface position may be assumed, for design purposes, to be the distancealong axis 66 between the transducer surface and the plane defined bythe distal ends of bolsters 42 and 48. The ability of the signalacquisition circuitry to effectively acquire the acoustic signalradiated from the test material surface and distinguish that signal fromnoise may depend on factors such as the air gap distance, the signalacquisition circuitry's dynamic range (e.g. 48 dB in the presentexample), and the construction of the microphone. In a given design, thegap may be selected through testing of a particular device on testmaterial surfaces to accommodate expected variations in the testmaterial surface (as described in more detail below), while permittingthe acquisition of a sufficient acoustic return signal to detect defectsin the test material in view of the device's signal acquisitioncircuitry and the analysis algorithm used to detect the defect.

In the presently-described embodiments, and for purposes of example butnot limitation, the system can identify material defects utilizingvarious suitable signal analysis methods, for example based on signalmagnitude or frequency. As indicated above, an impact from the impacthammer may create multiple types of waves in the test material, forexample, primary waves (“p-waves”), shear waves (“s-waves”), andRayleigh waves (“r-waves”). As should be understood, p-waves and s-wavespropagate into the solid material along spherical wave fronts, with thep-wave defining a compression wave pattern in the direction of thewave's propagation and the s-wave defining a wave that varies in adirection normal to the propagation direction. R-waves are surface wavesthat propagate outward from the impact point and that can also becreated on the opposing side of the test surface by the p-waves ands-waves. It will also be understood that the speed at which the varioustypes of waves propagate in a given material varies with respect to eachother. Thus, for example, s-waves propagate at a speed slower than thespeed at which p-waves propagate. Considering, for example, a compositematerial used in the construction of aircraft fuselages wings, controldevice surfaces, rotary blades, engine nacelles, radomes, and turbinefan blades, constructed of a carbon fiber-reinforced polymer compositesheet separated from a similar composite sheet by a honeycomb aluminumcore sandwiched between and bonded to the opposing carbon fibercomposite sheets, for example as illustrated in FIG. 5, any one or moreof mechanical disbonding between the major layers of the material,delaminations within the composite sheets, crushing of all or a part ofthe aluminum core, thermal degradation and voids can cause thedevelopment of standing waves in the material arising from the variouswaves imparted to the material by the hammer. Standing waves can developbetween the test material surface and the opposing surface and/or suchdefects. These standing waves can be detectable at their resonantfrequencies or based on signal magnitude. The thickness of the testmaterial for which the device as described herein can detect defectsthrough the entire thickness will vary with the materials andconstruction of the test material, e.g. depending on the thickness andlayers of the (for instance, carbon fiber) front and back surfacesheets, the type of honeycomb inner material (e.g. aluminum or NOMEX),the honeycomb structure's thickness, and whether or not the testmaterial is perforated.

Microphone 60 in these embodiments utilizes an electric condensermicrophone transducer generally capable of detecting acoustic signals upto about 30 kHz, and in the presently-described embodiments theeffective range of microphone 60 may be considered to be from about 2kHz to about 25 kHz. At such a frequency range, the system comprised ofthe microphone and the processing circuitry that processes signals fromthe microphone operates at a resolution capable of detecting defectshaving a minimum dimension of about 0.5 inches by about 0.125 inches, orabout 0.25 inches by about 0.25 inches, in an orientation transverse tothe waves' travelling direction, or parallel to the transducer receivingsurface. As described above, the microphone transducer can be offsetfrom the test material surface, so that an air gap separates the two.Although either omnidirectional or unidirectional microphone transducersmay be used, unidirectional transducers are used in thepresently-described embodiments in testing composite materials havingsurfaces that are not perforated, while omnidirectional transducers areused with materials having perforated surfaces.

The data acquisition circuitry of unit 14 collects signal output datafrom microphone 60 (via signal acquisition unit 12) at a samplingfrequency of about 500 kHz. For each impact of the test material surfaceby hammer 54, the circuitry of data acquisition unit 14 collects 1,024data points for analysis (although, as noted below, the data collectionrate may be changed in certain embodiments at the user's selection).Signal acquisition unit 12 preamplifies and uploads analog data to dataacquisition unit 14, which digitizes the signal and uploads thedigitized information to processing unit 16 for analysis by theapplication program that executes at unit 16. In one of the embodimentsdiscussed herein, the application at unit 16 determines the maximumpeak-to-peak voltage difference in the signal and compares that value toa predetermined primary threshold and a predetermined secondarythreshold. In response to the comparison, the processing unit displaysinformation describing the result at screen 102 and also sends aninstruction to the data acquisition unit, which relays the instructionto the signal acquisition unit, to thereby cause the signal acquisitionunit to activate one of the LEDs 72 at the top surface of unit 12. Asdiscussed above, there are three colors of LEDs 72—green, yellow andred. If the peak-to-peak signal is above the primary threshold but belowthe higher, secondary threshold, the instruction causes the signalacquisition unit to actuate the yellow LED 72. If, however, the signalis above both the primary and secondary threshold levels, the signalcauses the signal acquisition unit to actuate the red LED 72, indicatinga significant defect. If the peak-to-peak voltage of the acquired signalis below the primary threshold, the instruction signal to the signalacquisition unit causes the signal acquisition unit to actuate the greenLED 72, indicating a likelihood that a defect has not occurred.

To calibrate the system for amplitude-based signal analysis, the userselects a sample of the material that will be tested but that the userknows has no defects and places the signal acquisition unit onto thetest material surface so that the distal ends of the bolsters engage thesurface. The user begins a test through a “calibrate” button provided bythe application's graphical user interface at screen 102 and starts thehammer and microphone either by actuating start/stop button 74 on unit12 or activating a button in the graphical user interface provided byunit 16 on touch screen 102. This actuation signal causes the signalacquisition unit processor (in automation mode) to drive the hammer at arate of about eight to about ten, and in this example eight, strikes perminute. Microphone 60 receives acoustic signals from the test materialresulting from the hammer blows. Preamplifier 136 adjusts the analogsignal level, and data acquisition unit 14 thereby receives the analogsignal from the microphone via preamplifier 136 and cable 134. Thecircuitry of data acquisition unit 14 identifies the beginning of eachsignal spike (i.e. the beginning of each portion of the measurementsignal corresponding to a hammer tap), and then acquires a number ofdata points (e.g. 1024, 2048, or 4096) at a sampling rate (e.g. 500 kHz)as selected by the user at step 150, as described herein with respect toFIG. 4. A default setting in these embodiments is 1024 data points at asampling rate of 500 kHz, so that data acquisition unit 14 acquires anddigitizes the analog measurement signal for an approximately twomillisecond (2.048 millisecond) period following the detection of eachincoming hammer tap. The collected digitized data for each twomillisecond period is referred to herein as a test block of data.Processing unit 16 receives the digitized time-domain signal from dataacquisition unit 14. The processing unit's processor, under control ofthe application, determines the peak-to-peak voltage of the digitalsignal for each received test block of data and displays the voltage ona display provided by touch screen interface 102 as the test blocks arereceived and processed by unit 16.

The particular value of the displayed output depends not only upon thesignal data, but also upon the active range of the signal processingcircuitry of data acquisition unit 14 and the gain applied to theacquired signal within that circuitry. In the present embodiments, thesignal acquisition circuitry of data acquisition unit 14 has an activerange from 0 mV to 850 mV. Thus, the peak-to-peak value determined bythe application at unit 16 for each given test data block and displayedat screen 102 is a value between 0 and 850 mV peak-to-peak, asdetermined by the signal data and the gain that the circuitry of dataacquisition unit 14 applies to that signal. The programming of theapplication executed by the processor of processing unit 16 compares thepeak-to-peak voltage level of the acquired signal for each test datablock to the predetermined (and stored, in memory of unit 16) primarythreshold level and secondary threshold level, each defined in theapplication as a selectable mV level, or alternatively as a percentageof the device's overall active range. Depending on the comparison, theprocessing unit sends a signal to signal acquisition unit 12 via dataacquisition unit 14 to actuate the corresponding red, green, or yellowLED 72. In this example, the predetermined primary threshold level is500 mV, while the secondary threshold is 600 mV. In another embodiment,the secondary threshold is omitted, so that only the 500 mV primarythreshold is used and so that only the green and red LEDs of LEDs 72would be actuated.

At initiation of the calibration, signal acquisition unit 12 will havean existing gain and an existing hammer impact strength, for example setduring the system's original configuration or by a previous calibration.Signal acquisition unit 12 actuates the hammer and applies the gain tothe resulting signal received by microphone 60 and passed up to dataacquisition unit 14, causing a display of the resulting peak-to-peakvoltage at display 102 and the actuation of a green, yellow or red LED72 (or green or red, if there is no secondary threshold or if it isoptionally omitted) on signal acquisition unit 12, depending upon theresult of the application of the signal peak value to the initialized500 mV and 600 mV primary and secondary thresholds. The user firstrefers to LEDs 72 for an initial, rough calibration. If the signalresults in actuation of a yellow or red LED (or, if no secondarythreshold is used, a red LED), then the hammer impact strength is toohigh, in that the system is indicating a defect exists when in fact thematerial has no defects. The user, however, can change the impacthammer's impact strength through actuation of buttons 30 or 32 on thesignal acquisition unit housing. These buttons are connected to a switchsystem that communicates with the signal acquisition unitmicroprocessor. The processor's programming is configured to recognizeactuations of button 30 as a request to decrease the solenoid power, andto interpret actuations of button 32 as a request to increase thesolenoid power. Thus, by pressing button 30, the user instructs thesignal acquisition unit processor to lower the power at which hammer 54taps the test material. Correspondingly, the user's actuation of button32 instructs the signal acquisition unit processor to increase thehammer impact force. As the user moves the impact power up or down, thesignal acquisition unit processor changes a display of the impact powerrating on display 26.

In this instance, since the user knows that the system is indicating adefect (i.e. by a red or yellow LED at 72), when in fact the testmaterial is known not to have defects, the user knows that the hammerimpact strength is too high, and so actuates button 30 to lower thehammer impact power, and repeats the test. If the LED 72 again showsyellow or red, the user again lowers the hammer impact strength andrepeats the process, continuing to do so until the test results in agreen LED 72. At the point when the LED display goes from yellow (orred) to green, the user has set the impact strength so that the system'suse with a sample of a test material of the type for which thecalibration is performed that has no defects will result in apeak-to-peak signal at processing unit 16 just below 500 mV, andtherefore a green LED output 72 at signal acquisition unit 12, while thesystem's use with such a sample having a defect will result in apeak-to-peak signal at processing unit 16 above 500 mV, and therefore ayellow or red LED output 72. Having achieved a hammer impact strengthresulting in a peak-to-peak signal just below 500 mV for a sample havingno defects, the user may then view the displayed numerical value of thepeak-to-peak voltage on display 102 and continue to reduce impact hammerstrength downward, if desired, to provide a buffer between a “normal”return signal and one that will trigger identification of a defect.

If the calibration signal initially results in a green LED 72,indicating that the return signal during the calibration test correctlyindicates that no defect is present, the user actuates button 32 toincrease the hammer impact strength and repeats the process until theacquired signal peak-to-peak voltage exceeds 500 mV, thereby changingthe LED display 72 from green to yellow (or red, if no secondarythreshold is used). At this point, the user views the actual voltageoutput on display 102, and actuates button 30 to lower the hammer impactstrength, repeating the process until the return signal moves back below500 mV peak-to-peak, thereby returning the LED display 72 to green, andpossibly further if a buffer distance is desired.

If the user is unable to successfully calibrate the signal by adjustinghammer impact strength in this manner, or if, having made an initialcalibration by adjusting hammer impact strength, the user wishes to makeadjustments at a finer scale, the user may also make adjustments to thegain applied to the microphone output signal by preamplifier 136. Toallow this functionality, the application operating on processing unit16 provides a user interface option at display 102 through which theuser may enter a numerical value for the desired pre-amplification levelor select from a list of predetermined level options, the entry orselection of which causes the processor at processing unit 16 tocommunicate a signal to the processor of data acquisition unit 14, inturn causing that processor to instruct the processor of signalacquisition unit 12 to accordingly adjust the gain applied by the SAU'spreamplifier 136 to the incoming microphone signal.

Additionally, the user may exchange the hammer 54 in the signalacquisition unit for one of greater or lesser mass/weight in order toapply a greater or lower impact force to the material, as test materialscan provide varying responses to hammers of different mass. For example,even if the user has successfully calibrated the device using hammerimpact force adjustment and/or gain adjustment, there may be a need tochange hammers for a given test material if the contrast difference,i.e. the difference in the measurement signal peak-to-peak voltage whenno defect is present and the peak-to-peak voltage when a defect ispresent, is either too large or two small. If, for example, with ahammer of a given mass, the contrast difference can range up to a highmV level (the difference is variable because different defects result indifferent voltage changes) as compared with the device circuitry'sactive range, the measurement signal could be too sensitive, givingfalse positives. If the contrast range is too small, some signalscorresponding to defects could be masked by noise. In certainembodiments as described herein, it is desired that this difference bewithin a range of 200 mV to 400 mV, but this acceptable range can varydepending on system parameters, for instance the circuitry's activevoltage range.

It should be understood that the hammer's impact force varies with thehammer's mass. In the presently-described embodiments, for example, thehammer comprises a solid member constructed of a phenolic thermosetplastic, but the hammer 54 is releasably secured within the solenoid 52,e.g. by set screws that secure a retractable retaining pin that retainsthe hammer, so that the hammer may be replaced as desired with hammersof the same shape and configuration but formed by different materialshaving different masses, so that the hammer mass, and therefore theimpact force, may be controlled by the user through selection of aparticular hammer. For example, hammers 54 may be made of polymermaterials having greater or lesser mass or, for example, from brass orother metals having varying masses. Thus, if the user wishes to adjustthe defect/no-defect peak-to-peak signal difference, the user mayoptionally replace the existing device hammer 54 with a hammer 54 havinggreater or lesser mass, depending on the direction of the desiredadjustment.

Having replaced the hammer, the user executes the calibration processagain to thereby move the output signal peak-to-peak voltage to justwithin the 500 mV peak-to-peak value, or to a buffer amount furtherbelow that level if desired, in the same manner as described above.Multiple hammer exchanges may be made. Still further, the applicationmay provide an interactive method through the graphical user interfaceprovided at display 102 by which the user may adjust the primary and, ifpresent, secondary thresholds up or down as desired to accord with thesignal results obtained from the impact hammer taps on the non-defectsample material. One or more of the methods described herein may bepracticed within a calibration of a given device.

Upon successfully achieving the desired signal response, the useractuates a “save” button in the application's user interface, causingthe application to save the calibrated hammer actuation or impactstrength (and, if applicable, adjusted gain and threshold value(s)and/or hammer selection) in memory at unit 16 in association with anidentifier (applied by the user as part of the calibration process) thatcorresponds to and uniquely identifies the test material undercalibration. Thus, for any given test material, the system stores inmemory a record that stores data items identifying the hammer impactstrength, signal gain, primary and secondary threshold values, andhammer identity, in association with the given test material for thepeak-to-peak amplitude test. If a user sets up a record for a given testmaterial without performing a calibration, the application initiallystores default gain, hammer impact force, thresholds, and hammeridentities, and these remain in place until the user saves new valuesupon calibration. The system is then ready to be used for testingactual, in-use material of the same type as the calibration testmaterial, in the manner as described herein.

As indicated above, however, the system may also be used in a mode bywhich the system analyzes acquired signals based on frequency. Forexample, and again assuming that data acquisition unit 14 acquiressignals at a sampling frequency of 500 kHz and 1024 data points perhammer tap, the signal acquisition unit uploads analog data to dataacquisition unit 14, which so digitizes the voltage-time signal. Foreach test data block, data acquisition unit 14 applies a windowing andfast Fourier transform (FFT) algorithm to thereby convert the signal tothe frequency domain. A Hamming window is used in this process, in thatit results in less ringing in the spectral values.

FIG. 3 illustrates an example of such a signal, acquired with amicrophone having an active range between about 2 kHz to about 25 kHz.Again, assume that the signal is acquired during calibration from amaterial known to have no defects. From testing and experience withmaterials of this type, it is known, for example, that defects result ina standing wave at a resonant frequency within a range of 2 kHz to about15 kHz. Thus, the portion of the signal above 15 kHz in FIG. 3 is onlyor primarily the result of noise. In a calibration mode, the systemapplication at unit 16 analyzes the test data block signal from 2 kHz to15 kHz, finding the frequency at which the peak value occurs, in thisinstance about 2.5 kHz. Because this material is known to have nodefects, the 2.5 kHz peak indicates that the resonant frequency of thestanding wave produced in the test material between the surface at whichthe hammer strikes the material and the opposite surface, is 2.5 kHz.

The user may also test the device with a sample of the same materialhaving a known defect. This also results in a signal analyzed by thesystem such as shown in FIG. 3, except that the peak resonant frequencyoccurs at a different frequency. The difference, or contrast, betweenthe peak resonant frequency in the no-defect sample and the peakresonant frequency in the defect sample illustrates the scale of themagnitude of the frequency shift the system should be able to identifyin distinguishing materials having no defects from those having defects.In examining later samples, the system will compare the detected peakresonant frequency with the stored calibrated (no-defect) frequencyvalue, so that peak resonant frequencies that are within a calibratedthreshold distance (in frequency) from the calibrated frequency valueare considered not to identify defects, while those outside thethreshold frequency distance identify defects. Thus, given theidentified frequency difference between the two peak resonantfrequencies in the calibration, the user can select a frequencythreshold difference value within that distance that is just beyond anormal expected variance. As in the peak-to-peak amplitude/voltageexample, however, it may be desired to have more separation between thenon-defect peak sample resonant frequency and the defect peak sampleresonant frequency, to assure that the variety of possible defects aredetectable and distinguishable by the system. Thus, the user can adjustthe pre-amplifier gain, hammer impact strength, and possibly hammeridentity, in a similar manner as described above, and the user can thenre-test the no-defect and defect samples, repeating the process untilthe two tests present an acceptable contrast between the defect andno-defect peak resonant frequencies. At this point, the user selects thethreshold frequency difference and enters this value to the processor ofunit 16 via a user interface screen presented at display screen 102.

Also in response to user instruction through the interface during thecalibration, the system application at unit 16 measures the amplitudevariation in the no-defect sample signal from 15 kHz to 25 kHz,determines the mean signal value and the standard deviation in thesignal data from that mean value. The processor of processing unit 16stores the no-defect sample resonant frequency (in this example 2.5 kHz)as the calibrated normal resonant frequency for the selected material,and also stores the mean noise value and the standard deviation, as wellas the calibrated pre-amplifier gain, hammer impact strength, thresholdvalue(s), and hammer identity as part of the calibration parameters forthe corresponding test material under the frequency-based analysis testoption.

Thus, as with the peak-to-peak calibration procedure, the user mayconduct frequency-based calibration procedures with various materials,storing each set of calibration values in association with an identifiercorresponding to a particular material. Moreover, the user may calibratethe same test material both for peak-to-peak amplitude-based andfrequency-based analysis, storing both options at unit 16 in associationwith the material identifier so that the respective set of calibrationparameters is stored in the test material record in association with thecorresponding test option, so that when the user later selects oneoption or the other by which to test a given material, the system canpull the calibration parameters associated with the selected materialand test option and configure the system according to the correspondingparameter instances. A user may wish to test the same material sampleboth under the peak-to-peak method and the frequency method.

Although the present discussion anticipates that an end-user may performthe calibration procedures discussed herein, these procedures may alsobe performed by the manufacturer as part of the manufacturing process,storing the relevant calibration data in the device in association withrespective test material and test option identifiers, for later use ofthe device by the end-user.

As noted, when the end-user uses system 10 to test a given material, theuser identifies the test material and the desired analysis optionthrough the graphical user interface provided at screen 102. Uponreceipt of the selection, processing unit 16 selects the calibrationparameters associated with the selected material for the selectedanalysis option. For purposes of this discussion, assume the userselects the frequency option. When the user thereafter uses the systemto test a material sample, and signal acquisition unit 12 provides theresulting voltage-time test data block signals to data acquisition unit14, data acquisition unit 14 digitizes each test data block signal andapplies the Hamming window and FFT algorithm to produce a signal such asis shown in FIG. 3. Data acquisition unit 14 forwards the resulting datato processing unit 16. The application at unit 16 then determines thepeak resonant frequency and compares that frequency to the calibratedpeak resonant frequency value. If a defect is present in the material,the detected peak resonant frequency will be different from the peakfrequency expected if no defects are present by an amount at least aslarge as the stored calibration frequency difference. This occursbecause a defect having a resolution within the range of the presentlydescribed embodiments will produce a peak response that is both of adifferent decibel level and at a different resonant frequency thanresults for the standing wave generated by the opposing side of thematerial. If the detected resonant frequency is offset from thecalibrated peak resonant frequency by more than the calibrated frequencydifference, processing unit 16 sends a signal to the data acquisitionunit that causes the data acquisition unit to send a signal to thesignal acquisition unit, causing the signal acquisition unit to actuatethe red LED 72, indicating a defect.

In this embodiment, a secondary threshold frequency difference is notused, although it should be understood that a secondary threshold couldbe used, for example established as a predetermined distance away fromthe calibrated peak resonant frequency. In such an embodiment, if thedetected peak resonant frequency is offset from the initial calibratedpeak resonant frequency by an amount greater than the stored primarythreshold difference, but not by more than the secondary thresholdfrequency difference, processing unit 16 sends a signal to dataacquisition unit 14, which sends a signal to signal acquisition unit 12,causing signal acquisition unit 12 to actuate the yellow LED 72,indicating an intermediate defect. If the detected peak resonantfrequency is offset from the calibrated peak resonant frequency by lessthan the initial, primary threshold frequency difference amount,processing unit 16 sends a signal to signal acquisition unit 12, viadata acquisition unit 14, causing the signal acquisition unit to actuatethe green LED 72.

Other tests may be applied to the frequency domain data. For example,during calibration of the system for multiple samples of the samematerial, where the samples have varying defects, the testing may revealthe occurrence of signal peaks at consistent frequencies respectivelycorresponding to various types of defects. The user may save thesefrequency markers within the memory of processing unit 16 through dataentry via the graphical user interface at display screen 102. When theprocessing unit receives a test data block from data acquisition unit14, the processing unit application locates the resonant frequencypeak(s) and compares the corresponding frequency(ies) to the storedfrequency markers. If the test data block has one or more peak resonantfrequencies at or sufficiently close to corresponding stored frequencymarkers, the application determines that there is likely a defect and,accordingly, sends a signal to signal acquisition unit 12 via dataacquisition unit 14 to activate the red LED 72. If there are no peakresonant frequencies at or close to a stored frequency marker, theapplication sends a signal to signal acquisition unit 12 to activate thegreen LED 72.

Still further, the application at processor 16 can determine the meansignal value in the test data block from 2 kHz to 15 kHz and comparethat detected value to the calibrated mean signal value saved for theno-defect sample for the material under test. If the presently detectedmean signal value is greater than the calibrated mean signal value by anamount greater than the calibrated standard deviation, this indicatesthe possible presence of a defect in the material under test,particularly for far side disbonds.

Varying embodiments of the system described herein use one or more ofthese tests in determining whether a defect is present in a materialunder test. For example, in some embodiments, the system uses only thepeak resonant frequency shift test, while in other embodiments, thesystem detects a defect only if the frequency shift test indicates adefect and at least one of the frequency marker test and the mean signalvalue test also indicates presence of a defect, while in still furtherembodiments the system determines presence of a defect if any one of thethree tests indicates a defect. Thus, it should be understood thatvarious analyses may be implemented.

As indicated above, the user begins a test, whether in calibration modeor actual test mode, by actuating start/stop button 74. This causescircuitry on board 22 to energize the coil in solenoid unit 52,overcoming the internal spring bias to thereby move hammer 54 downwardalong axis 68 away from face 44 and toward the surface of the testmaterial. In the presently-described embodiments in an automation mode,the circuitry at board 22 repeatedly actuates solenoid unit 52, so thatsolenoid unit 52 repeatedly drives hammer 54 downward along axis 68 tostrike the test surface, and so that between such strikes or taps, thespring internal to the housing of solenoid unit 52 returns hammer 54along axis 68 and away from the test material surface, in preparationfor the next tap. The tap and return cycle occurs, for example, eighttimes per second, or at a 125 millisecond period. Because the electricalpower used to drive solenoid unit 52 is drawn from the batteries securedto tray 84, the potential of those batteries (e.g. 7.6v for rechargeablebatteries, up to 14v) defines the baseline power at which hammer 54 maybe driven to tap the test material surface. The signal acquisition unitprocessor, on board 22, controls the duty cycle of that 125 millisecondperiod to control, through pulse width modulation, the power applied tothe hammer by solenoid 52. In the presently-described embodiment, theprocessor controls the control circuitry so that the duty cycle isvariable between 2% and 50%. That is, the duty cycle is variable so thatthe power control circuitry applies the battery across the solenoid coilwithin a range of 2.5 milliseconds to 62.5 milliseconds out of the 125millisecond period. As should be understood in view of the presentdisclosure, the high part of the duty cycle, i.e. the percentage of theduty cycle at which power is applied to the solenoid coil, contributesdirectly to the force with which the solenoid drives hammer 54 downwardalong axis 68. Thus, by controlling the duty cycle within the 2% to 50%variable range, the device directly varies the hammer's impact force.

In that regard, the signal acquisition unit processor, having controlover the solenoid's impact force, drives LED display 26 to display anumber indicating the signal acquisition unit's hammer force (whichcorresponds to duty cycle setting) at any given time. For example, theprogramming of the signal acquisition unit processor may convert the 2%to 50% duty cycle scale to a scale of 0 to 100, with 2% duty cyclecorresponding to 0 and 50% corresponding to 100. At any time during thesystem's operation, and as described above, the user can change theimpact hammer's impact force through actuation of buttons 30 or 32 onthe signal acquisition unit housing. These buttons are connected to aswitch system that communicates with the signal acquisition unitmicroprocessor. The processor's programming is configured to recognizeactuations of button 30 as a request from the user to decrease thesolenoid power, and to interpret actuations of button 32 as a request toincrease the solenoid power. Thus, by pressing button 30, the userinstructs the signal acquisition unit processor to lower the solenoidpower duty cycle, thereby lowering the power at which hammer 54 taps thetest material. Correspondingly, the user's actuation of button 32instructs the signal acquisition unit processor to increase the solenoidduty cycle and thereby increase the hammer impact force. As the usermoves the impact power up or down, the signal acquisition unit processorchanges the displayed impact power rating on display 26 to maintaincorrespondence with the duty cycles selected by the user.

The signal acquisition unit may also automatically adjust the solenoid'sduty cycle, and therefore the hammer's impact force, based on the outputof an inertial measurement unit (IMU) mounted on board 22. Theconstruction and operation of inertial measurement units should beunderstood, and is therefore not discussed in detail herein. As shouldbe understood, an IMU outputs data representative of the device's pitch,roll, and yaw with respect to an initial condition, e.g. in which hammer54 and its axis 68 are vertically aligned, the hammer distal end isdirected downward, and the plane defined by the distal ends of feet 42and 48 is horizontal.

Given a particular hammer mass, solenoid duty cycle, gap distance, andhammer stroke, as described above, the force at which hammer 54 strikesthe material test surface will also vary correspondingly withgravitational effects over the signal acquisition unit's threedimensional orientation. The orientation's most positive effectcorresponds to the greatest hammer force when axis 68 is directlyvertical and when the distal end of hammer 54 is facing downward.Conversely, the orientation's most negative impact on hammer impactstrength occurs when axis 68 is vertical but the distal end of hammer 54is pointing directly upward. The gravitational effect varies betweenthese extremes over the various pitch, roll, and yaw variations betweenstraight up and straight down. These variations are determined throughcalibration and are stored in a lookup table accessible by the signalacquisition unit microprocessor in memory. The table stores incrementalpitch, roll, and yaw ranges, or zones, between the zero degree and 180degree extremes, and respectively associates the increments withadjustments in solenoid duty cycle as determined by the calibrationprocess.

When the user begins a test by actuating start/stop button 74, thesignal acquisition unit processor detects the pitch, roll, and yawoutput of the IMU, selects the duty cycle adjustment corresponding tothe stored pitch, roll, and yaw increment zone within which the actualpitch, roll, and yaw falls, and adjusts the calibrated solenoid dutycycle accordingly.

As described above, the hammer's impact force varies with the hammer'smass. In the presently-described embodiments, for example, the hammercomprises a solid member constructed of a phenolic thermoset plastic,but hammer 54 is releasably secured within solenoid 52, by set screwsthat secure a retaining pin that retains the hammer, so that the hammermay be replaced as desired with hammers of the same shape andconfiguration but formed by different materials having different masses,so that the hammer mass, and therefore impact force may also becontrolled by the user through selection of a particular hammer. Forexample, hammers 54 may be made of polymer materials having greater orlesser mass or, for example, from brass or other metals having varyingmasses.

The discussion above has assumed that the test material surface isperfectly planar. Often, however, the test material surface will becurved, for example as is the case for materials used in theconstruction of many aircraft components. Surface curvature, whetherconvex or concave, or other deviations from a perfectly planar surfacecan cause variations in the distance between the receiving transducersurface of microphone 60 and the test material surface as the signalacquisition unit is moved to different positions on the test materialsurface during use. Such surface height variations may cause thesystem's response to vary from what it would be with a planar sample ofthe test material (assuming the system was calibrated with a planarmaterial). For example, assume the signal acquisition unit is placedover a portion of the test material surface that has a high point. Thegap between the hammer and the microphone transducer is less than itwould be if the test surface were flat, causing the hammer to strike thesurface with a higher force and the microphone to receive the resultingacoustic signal at a greater intensity. On the other hand, depressionsin the test material surface can have the opposite effect.

Where the signal acquisition unit is intended for use with testmaterials having generally known curvatures, the device may beconstructed to minimize distances between adjacent bolsters 42/48 tothereby minimize variability in the gap between the test materialsurface and the microphone transducer and hammer. Referring again toFIG. 1B, consider each of bolsters 42 and 48 to define a longitudinalaxis extending parallel to axes 66 and 68 and extending through thecenter of the respective bolster. Considering respective distances, indirections transverse to these axes, between the axes of bolsters 42(0.44 inches in one embodiment), between the axes of bolsters 48 (again,0.44 inches in the same embodiment), between the axes of the respectivebolsters 42 and 48 on clamshell half 17 a (2 inches in the sameembodiment), and between the axes of bolsters 42 and 48 on clamshellhalf 17 b (2 inches in the same embodiment), and the two distancesbetween the axes of the diagonally arranged bolsters 42 and 48, thehousing formed by clamshell halves 17 a and 17 b, the placement of thebolsters in the housing, and the maximum hammer travel (⅜ inches in thesame embodiment) are selected so that when the signal acquisition unitis used on the test material, the material's convex surface formationsdo not extend sufficiently far into the gap between the planar surfacedefined by the bolster distal ends and the microphone/hammer toinvalidate the system's calibration and so that the material surface'sconcave formations do not move sufficiently far from the hammer and thetransducer from that ideal planar surface to invalidate the originalcalibration. Where a material has areas of curvature that negate thedevice's original calibration to a flat surface, the system may beseparately calibrated to the same material, but on a sample of suchmaterial having the expected curvature. Such calibration may result, forinstance, in hammer impact strengths, gain, and/or hammer identities orother calibration parameters that differ from those parametersdetermined by an original calibration for the same material in a flatconfiguration. This calibration is then separately stored in the device,as described above, so that the user can select the stored calibrationfor the given curved surface when the need arises to test such asurface. Also, it should be understood that where the test materialsurface curves in only one dimension, it may be possible to orient thesignal acquisition unit on test material so that the test occurs on asurface with lesser effective curvature.

The present system may also be used to record test data in associationwith relative spatial reference information. The system stores each testresult in association with the underlying signal data that generated theresult and with three dimensional position data that identifies a pointat which the test data was acquired within a three dimensionalcoordinate system common to the position data for the other test pointstaken on the same test material surface. A three dimensional scan of thetest surface may also be acquired, in association with the same threedimensional coordinate system, and provided to an independent computersystem that may, in turn, display the test material surface withindicators identifying the positions on the surface at which the testswere taken, with icons (which may be color coded correspondingly to thered/green or red/yellow/green presentation of LEDs 72) indicating therespective test results (i.e. pass, intermediate defect, and significantdefect).

More specifically, prior to executing a series of tests on a given testmaterial, the user mounts a local positioning system, in this instance athree dimensional scanner device, in a fixed position with respect toand proximate the test material so that the scanning device images theentire area of the material surface that will be tested. An example ofsuch a scanner is the three-dimensional infrared scanner sold under thename FREESCAN by NDT Consultants Limited, of Coventry, United Kingdom.The scanner illuminates the test material surface over which an activereflector is moved, receives reflected data at two cameras that areoffset from each other within the scanner system, and based ontriangulation of the reflected data received by the cameras, createsdata describing a portion of the test material surface within a threedimensional coordinate system. Thereafter, the scanner monitors thecameras, which are infrared-sensitive, having the test surface in theirfields of view. When the user, having now placed the signal acquisitionunit at a given position on the test material surface within the scannerfield of view to conduct a test, actuates button 74 to start that test,the signal acquisition unit's processor actuates infrared transmitter 70on the top of unit 12, thereby causing transmitter 70 to emit aninfrared signal detectable by the scanner cameras. The scanner camerasdetect the signal and determine the position of the infrared transmitterin the same three dimensional coordinate system in which the testsurface material scan is defined.

The scanner then transmits the three dimensional coordinates toprocessing unit 16, via a short-range wireless communication between thetwo devices, for example under the BLUETOOTH protocol. Having receivedthe position information from the scanner, and having also received thetest data from the signal acquisition unit and the data acquisitionunit, as described herein, from the test that generated the positiondata, the processing unit stores the test data, the test data results(i.e. whether the test data indicated presence of a defect according toa methodology such as described above), and the position data inassociation with each other in a discrete data record or file in memoryat the processing unit. The user then moves unit 12 to the next positionon the test material at which it is desired to test for defects. Theprocess repeats, such that processing unit 16 acquires position data andtest data for the second test position. This process repeats for as manytests as the user wishes to make. As a result, the processing unit hasstored each incremental portion of test data, the result of theapplication of the test data to the defect identification analysisdescribed herein, and the position data, for each respective test pointon the test material surface. The association of each set of test pointdata with a respective position in a common three dimensional coordinatesystem, in which the scan image of the test material surface is alsolocated, allows an independent computer system to create an image of thethree dimensional test material surface scan, correlate the stored testdata to positions on the scan surface, and indicate on a displayed imageof the scanned test material surface whether a defect occurred at eachrespective position. The independent computer system, which receives thestored test data (including the three-dimensional position data) fromprocessing unit 16, e.g. via a wireless connection as discussed above orother method such as via the processing unit's USB port or a removablememory such as a microSD card, and the test material scan data from thescanning device, presents an image on a display screen of the testsurface, with the indication at each point on that surface at which atest has occurred, whether the test passed or failed, and if failureoccurred whether the defect was intermediate or significant. Icons canbe used as desired to represent such conditions at each surface point.This provides the user viewing the screen to visually and intuitivelyidentify the location of each test result on the surface image.

Accordingly, system 10 provides information to the user regardingpossible defects in the material, not only through real-time actuationof LEDs 72 and the display on screen 102, indicating to the user whethera defect has occurred, but also by downloading to a remote computingdevice a data set that locates the test data within a common threedimensional reference system so that the test data can be located on animage of the test material surface itself.

FIG. 2 illustrates the general electronic organization of the circuitryof signal acquisition unit 12 that is mounted on board 22. A processor118 drives LED display 26 via an LED driver (not shown). A membraneswitch, indicated generally at 120, defines up and down buttons 30 and32 (driven by field effect transmitters on board 22), start/stop button74, and LEDs 72. Again, microprocessor 118 drives LEDs 72 viaappropriate LED drivers.

Microprocessor 118 drives solenoid unit 52 via a boost converter 122that is powered by the batteries stored at tray 84. Microprocessor 118also communicates with IMU 124 and drives infrared transmitter 70, inthe manner as described herein. As described above, infrared transmitter70 communicates with local positioning system 126 via an infrared signalcommunication path, indicated at 129. Local positioning device 126communicates with processing unit 16 via BLUETOOTH wireless connectionindicated at 130.

FIG. 2 also illustrates the general electronics configuration of dataacquisition unit board 76. Microprocessor 118 and microphone 60 of thesignal acquisition unit communicate with a microprocessor 132 of thedata acquisition unit via cable connection 134 between connectors 128and 40 on the data acquisition unit and the signal acquisition unit,respectively. The signal acquisition unit drives the cable communicationto the data acquisition unit via preamplifier 136. Upon detecting theincoming signal from cable 134, an input selector relay 138 at unit 14directs the signal to an amplifier module 140 and an analog-to-digitalconverter 142. The digital data is stored in a static random accessmemory 144, from which microprocessor 132 retrieves the data, detectsthe beginning of test data blocks, performs post-processing, if any (forexample, by applying a Hamming window and fast Fourier transform inembodiments in which signal analysis is conducted in the frequencydomain), and outputs the digitized test data blocks to processing unit16 via a high speed USB device 146 and cable that passes through conduitline 98.

FIG. 4 (and also with reference to the system components described withrespect to FIGS. 1 and 2) illustrates the operation of system 10, insequence form. At 148, a user has actuated on/off button 74 of the dataacquisition unit, sending a signal to microprocessor 132 that causes themicroprocessor to send a signal via USB device 146 and cable 98 toprocessing unit 16, causing the processing unit to actuate a power upsequence. Alternatively, the user can actuate the power-up mechanism onthe smartphone processing unit itself. In either instance, actuation ofdevice 16 initiates the application program that resides on unit 16.

At 150, the processing unit application program presents a graphicaluser interface at screen 102 through which the user may select variousoptions for conducting the test. For example, the user may select thetest rate, i.e. the rate that hammer 54 impacts the surface—eight timesper second in the example described above, or for example ten times persecond. The user may also select the number of data points (e.g. 1024,2048, or 4096) for which the circuitry of data acquisition unit 14collects at each hammer impact, and the rate at which those data pointsare sampled (e.g. 500,000 samples per second in the examples above, oras otherwise selected by the user at step 150). The user may also selectthe test material and the analysis algorithm that will be used toanalyze the data acquired by the system acquisition unit and processedby the data acquisition unit. As described in more detail above, forexample, the algorithm may analyze the test data based on peak-to-peakvoltage or by resonant frequency shift. The user may also select whetherprocessing unit 16 not only visually displays the test output data onscreen 102 and instructs the signal acquisition unit to display theresult via LEDs 72, but also to store the test data and position data atprocessing unit 16 for later download to a remote computing system.Audio effects may be provided, for example issuing varying audio signalsdetectable by the human operator in response to test data, correspondingto the green, yellow and red LEDs 72. The user may also select whetherthe test will be in a single tap mode, in which the hammer makes only asingle impact of the test material, or automation mode, in which thehammer continuously impacts the test material surface, until the userinstructs the test to end.

As described above, the user will have determined the appropriate hammerimpact strength, hammer identity, threshold value(s), and/or signalamplifier gain to apply to test signals from the particular materialunder test, for the peak-to-peak test, and normal resonant frequency,mean noise value, standard deviation, gain, hammer impact strength,hammer identity, and threshold value, for the frequency-based test forthe same material. These setting or parameter records may be stored in alookup table in memory at processing unit 16, and at step 150 thegraphical user interface in this instance provides a lookup option bywhich the user may select an identifier corresponding to the particulartest material, and then provides an option by which the user selects thetest analysis option for the selected material. Upon receiving theuser's selections for these options from the user interface, theprocessor of processing unit 16 selects the corresponding set ofcalibration parameters. As noted above, for example, the calibrationdata includes hammer identity, and the unit 16 processor drives (via theapplication) the user interface to display the hammer identity from theselected calibration data, so that the user may install the correcthammer for the test. To set the gain identified in the record,processing unit 16 sends (at step 156) a corresponding signal to SAUprocessor 118 via DAU processor 132 at step 174, which in turnconfigures preamplifier 136 to the proper gain at step 176. To set thehammer impact strength, processing unit 16 sends (at step 156) acorresponding signal to SAU processor 118 via DAU processor 132 at step174 so that processor 118 thereafter actuates the solenoid at step 176at the desired strength level when impacts are required in the stepsdescribed below. Alternatively, as indicated at 152, the application atprocessing unit 16 may drive the graphical user interface at display 102to display the hammer impact strength and gain from the calibration datafor the test material and test analysis option the user selects, so thatthe user may manually configure the SAU to the appropriate hammer impactstrength through actuation of buttons 30 and 32 and manually configurethe gain through up/down buttons available on user interface 102(causing the processing unit to then send instructions to SAU processor118 at 174 to correspondingly configure preamplifier 136 at 176).Processing unit 16 uses the remaining calibration parameters inanalyzing the test measurement signals as described herein.

Even where the processing unit automatically sets the system accordingto the calibration data, the user may, at step 152, further adjust thehammer impact strength through actuation of buttons 30 and 32 on thesignal acquisition unit (to thereby set the solenoid duty cycle), iffurther adjustments are desired. Also at 152, the user may select andinstall a desired hammer 54 based on the mass and stroke lengthappropriate for the material under test, as determined by calibration.

At 154, the user has placed the signal acquisition unit in the operativeposition on a test material (see FIG. 5), so that bolsters 42 and 48rest upon the test material surface, and begins a test either byactuating a start button provided through the user interface on touchscreen 102 or by actuating start/stop button 74 on the signalacquisition unit. If the user actuates start/stop button 74 on unit 12,microprocessor 118 forwards a corresponding signal to microprocessor 132of the data acquisition unit as described above. Microprocessor 132 thenforwards the signal to processing unit 16. If the user actuates the testthrough the user interface screen, processing unit 16 receives theinstruction directly. Following either event, processing unit 16responds, at 156, by sending an instruction to processor 132 of the dataacquisition unit via cable 98, notifying the data acquisition unit thata test has begun and providing the signal gain settings to apply to thedigitized data.

At 174, microprocessor 132 forwards a notice signal to microprocessor118 of the signal acquisition unit via cable 134, instructing the signalacquisition unit to begin the test. The calibration data for hammerimpact strength and gain selected and/or received at steps 150 and 152are provided to microprocessor 118 at this time via this transmission.At 176, microprocessor 118 reads the output of IMU 124, determining theIMU's pitch angle, roll angle, and yaw angle and converting thisinformation to the orientation of signal acquisition unit 12.Accordingly, at 176, microprocessor 118 sets the duty cycle of boostconverter 122 to the hammer impact strength duty cycle selected by theuser or identified in the selected calibration data, adjusted based onthe lookup table accessed by processor 118 in response to theorientation of signal acquisition unit 112 as indicated by IMU 124.

At 178, microprocessor 118 actuates solenoid 52 via boost converter 122.If the user selected a single tap test at step 150, the SAU actuates theimpact hammer only once. If the user selected an automation test at step150, the SAU actuates the impact hammer solenoid 52 at a rate of eightimpacts per second, at the selected duty cycle, until a stop signal isreceived. Accordingly, while the system is in automation mode, the usermay pick up and move the signal acquisition unit from place to place onthe test material, or may simply slide the SAU across the test materialsurface, collecting test data in either case without having torepeatedly activate the start button to begin the hammer taps. Since thedata acquisition unit collects test data blocks from the resultingmovement signal in 1024 (or other selected) data point groups beginningwith detection of a measurable signal portion, the DAU and processingunit will acquire and accumulate test data as it is generated,regardless of the method by which the hammer is actuated or by which theSAU is moved over the test material surface.

At 180, processor 118 drives infrared transmitter 70 to transmitinfrared signal 129 to the local positioning system 126, causing localpositioning system 126 to determine the position of infrared transmitter170 within a predetermined three-dimensional coordinate system and totransmit the position data to processing unit 16 via wireless connection130.

Upon sending processor 118 the instruction to begin the test,microprocessor 132 of the data acquisition unit begins repeatedlymonitoring memory 144 for the arrival of test data from the signalacquisition unit. When microphone 60 receives a responsive audio signal,the microphone outputs the data to preamplifier 136, which amplifies andtransmits the data to input selector relay 138 via cable connection 134.As described above, the test data is amplified at 140, converted to adigital signal at 142, and stored in memory at 144. Accordingly, at step172, microprocessor 132 identifies the digitized test data blocks fromthe data at memory 144 and transmits the test data blocks to processingunit 16 via connection 98. Processing unit 16 applies the selected testalgorithm to the test data received from the data acquisition unit, atstep 172. At 157, processing unit 16 displays information at touchscreen 102 through the user interface, indicating whether the test foreach test data block results in an indication of no defect, anintermediate defect, or a significant defect. At 158, processing unit 16sends information corresponding to the test result to processor 132 ofthe data acquisition unit via connection 98. At 170, processor 132forwards the information to processor 118 via cable connection 134. At182, processor 118 identifies from the received information whether thetest result indicated no defect, an intermediate defect, or asignificant defect and drives LEDs 72 accordingly via membrane switch120. At 184, microprocessor 118 deactivates infrared transmitter 70.

At 160, processing unit 16 receives the position data associated withthe test from local positioning system 126, via wireless connection 130.As described above, processing unit 16 stores the test data receivedfrom signal acquisition unit and data acquisition unit 14 in associationwith the corresponding position information associated with the test sothat the data, so associated and also associated with the test result,can be downloaded to a remote computer.

At 162, the user indicates that the test has ended by actuatingstart/stop button 74 on signal acquisition unit 12 or by actuating acorresponding button through the user interface via touch screen 102. Ifthe system is in a single tap test mode, no further instructions to thedata acquisition unit are needed, and the application proceeds directlyto an exit step at 166. If the system is in automation mode, however,receipt of the step command at 162 causes processing unit 16 to sendanother initialization signal to data acquisition unit processor 132,and therefore signal acquisition unit processor 118, at 164, and dataacquisition unit 12 deactivates solenoid 52, thereby stopping the hammertaps, at 168. The application then exits the test routine at step 166.The system is, therefore, prepared for a next test so that when the userplaces signal acquisition unit 12 at the next desired test position onthe test material and begins a test by activating button 74 or acorresponding button at the user interface at screen 102, the testprocedure described herein repeats.

The software application at processing unit 16 may act as anintermediary between the user and/or other computers and the basiccomputer resources of processing unit 16, boards 22 and 76, andprocessors 132 and 118, as described, in suitable operatingenvironments. Such software applications include one or both of systemand application software. System software can include an operatingsystem, which can be stored on processing unit 16, and also processors118 and 132, that acts to control and allocate resources of thesecomputer systems. The application software takes advantage of managementresources by system software through program modules and data stored oneither or both of system memory and other memory sources, for example,mass storage.

Moreover, it will be understood from the present disclosure that thefunctions ascribed to processing unit 16, processor 132, and processor118 may be embodied by computer-executable instructions of a program,for example the application software and other programs discussedherein, that run on one or more of these computers. Generally, programmodules include routines, programs, components, data structures, etc.that perform particular tasks and/or implement particular abstract datatypes. Moreover, those skilled in the art will appreciate that thesystem/methods may be practiced with other computer systemconfigurations, including single-processor, multi-processor, ormulti-core processor computer systems, as well as personal computer andhand-held computing devices, microprocessor-based or programmableconsumer or industrial electronic, and the like. Aspects of thesefunctions may also be practiced in a distributed computer environmentwhere tasks are performed by remote processing devices that are linkedthrough a communications network. However, some aspects of the claimedsubject matter can be practiced on stand-alone computers.

Modifications and variations to the particular embodiments of thepresent invention may be practiced by those of ordinary skill in theart, without departing from the spirit and scope of the presentinvention, which is more particularly set forth in the appended claims.In addition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to belimitative of the invention so further described in such appendedclaims.

What is claimed is:
 1. A device for testing a test material for defectswithin the test material, the device comprising: a housing; an acousticbroadband transducer housed by the housing; a plurality of bolstersextending from the housing so that distal ends of the bolsters define aplanar surface that is offset from a receiving portion of the acousticbroadband transducer and so that the distal ends are unconnected to eachother within the surface; an impact member defining an impact portionand being housed by the housing so that the impact portion is movablefrom a retracted position to the surface, wherein the surface is offsetfrom the receiving portion of the acoustic broadband transducer by adistance at which the acoustic broadband transducer is capable ofacquiring acoustic waves across an air gap from a test material at thesurface, wherein the acoustic waves arise from impact of the impactportion of the impact member with the test material upon movement of theimpact portion of the impact member to the surface; and a processorsystem in communication with the impact member and the acousticbroadband transducer so that the processor system, in response toreceipt of an actuation signal, actuates the impact member to drive theimpact portion from the retracted position to the surface and so thatthe processor system receives a first output signal from the acousticbroadband transducer corresponding to the acoustic waves that arise fromimpact of the impact portion with a test material at the surface.
 2. Thedevice as in claim 1, wherein, between any two of the distal ends, thesurface is unobstructed by any structure attached to the housing.
 3. Thedevice as in claim 1, wherein the bolsters include respective rollerbearings at the distal ends.
 4. The device as in claim 1, wherein theprocessor system is configured to compare a magnitude level of the firstoutput signal to a predetermined level corresponding to possibleexistence of a defect in the test material.
 5. The device as in claim 4,wherein the processor system is configured to determine possiblepresence or absence of the defect based upon comparison of the magnitudeof the first output signal to the predetermined level.
 6. The device asin claim 5, further comprising a display in communication with theprocessor.
 7. The device as in claim 6, wherein the processor isconfigured to control the display to indicate the possible presence orabsence of the defect.
 8. The device as in claim 1, wherein respectivesaid distal ends define an area within the surface having a firstdimension and a second dimension orthogonal to the first dimension, andwherein the first dimension is about 0.44 inches and the seconddimension is about two inches.
 9. The device as in claim 1, furthercomprising a data port secured in the housing and in communication withthe processor system, wherein the data port is disposed on a surface ofthe housing transverse to the surface defined by the distal ends of thebolsters.
 10. The device as in claim 1, wherein the processor system isconfigured to respond to receipt of the actuation signal to actuate theimpact member to repeatedly drive the impact portion from the retractedposition to the surface.
 11. The device as in claim 1, wherein theprocessor system is configured to respond to receipt of the actuationsignal to actuate the impact portion to repeatedly drive the impact endfrom the retracted position to the surface at a rate of at least abouteight cycles per second.
 12. The device as in claim 11, wherein theprocessor system is configured to respond to receipt of the actuationsignal to actuate the impact device to repeatedly drive the impactportion from the retracted position to the surface at a rate within arange of about eight cycles per second to about ten cycles per second.13. The device as in claim 1, wherein the acoustic broadband transduceris an electronic condenser transducer.
 14. The device as in claim 1,comprising a microphone that contains the acoustic broadband transducerand wherein a system comprising the processor system and the microphonehas a resolution of about 0.125 inches in a plane perpendicular to adirection of travel of mechanical waves generated by the impact memberin the test material.
 15. The device as in claim 13, comprising amicrophone that contains the acoustic broadband transducer and wherein asystem comprising the processor system and the microphone has aresolution of about 0.125 inches in a plane perpendicular to a directionof travel of mechanical waves generated by the impact member in the testmaterial.
 16. A method for testing a test material for defects withinthe test material, comprising the steps of: providing a test devicecomprising a housing, an acoustic broadband transducer housed by thehousing, a plurality of bolsters extending from the housing so thatdistal ends of the bolsters define a planar surface that is offset froma receiving portion of the acoustic broadband transducer and so that thedistal ends are unconnected to each other within the surface, an impactmember defining an impact portion and being housed by the housing sothat the impact is movable from a retracted position to the surface,wherein the surface is offset from the receiving portion of the acousticbroadband transducer by a distance; placing the test device so that thedistal ends engage a test material at the surface; moving the impactportion of the impact member to the surface so that the impact portionof the impact member impacts the test material; and acquiring, via theacoustic broadband transducer, acoustic waves across an air gap from thetest material, where the acoustic waves arise from impact of the impactportion of the impact member with the test material.
 17. The method asin claim 16, further comprising determining possible existence of adefect in the test material in response to information provided acquiredfrom the acoustic broadband transducer corresponding to the acousticwaves acquired at the acquiring step.
 18. The method as in claim 17,wherein the determining step comprises comparing a magnitude level of anoutput signal from the acoustic broadband transducer corresponding tothe acoustic waves to a predetermined level corresponding to possibleexistence of a defect in the test material.
 19. The method as in claim16, wherein the moving step comprises repeatedly driving the impactportion from the retracted position to the surface.
 20. The method as inclaim 16, wherein the moving step comprises repeatedly driving theimpact portion from the retracted position to the surface at a rate ofat least about eight cycles per second.
 21. The method as in claim 16,wherein the moving step comprises repeatedly driving the impact portionfrom the retracted position to the surface at a rate within a range ofabout eight cycles per second to about ten cycles per second.